1. Field of Invention
The present invention relates to a method of fabricating a dielectric layer. More particularly, the present invention relates to a method of fabricating a carbon-rich low dielectric constant film.
2. Description of Related Art
Due to the rapid increase in circuit integration and functional integration, multi-layered conductive line systems with low dielectric constant material layers separating them are required. Conventionally, silicon oxide is used as the material constituting the dielectric layer. However, as the number of layers increases, overall thickness increases proportionately. Thickness can be reduced if the dielectric layer is made from a material having a lower dielectric constant. In general, the lower the dielectric constant of a dielectric layer, the thinner the dielectric layer is required to be to isolate the two neighboring conductive layers. Therefore, carbon-rich dielectric film, which has a lower dielectric constant than a conventional silicon oxide layer, is now routinely used in the fabrication of integrated circuits. The carbon-rich dielectric film is also capable of minimizing the effect of resistance-capacitance (RC) delay in a semiconductor circuit due to a narrowing of line width. In general, the carbon-rich low dielectric constant film is formed by plasma-enhanced chemical vapor deposition (PECVD) using gases having different carbon contents.
FIG. 1 is a flow chart showing the steps for producing a carbon-rich low dielectric constant film using a conventional PECVD process. In the PECVD, oxygen and nitrogen oxide plasma is used in the main deposition process. To prevent negatively charged particles in the plasma from depositing rapidly onto the dielectric film after plasma shut down, silicon-containing gases are first shut down after the main deposition process so that oxygen or nitrogen oxide plasma can still hold the negatively charged particles up a little longer. After a purging period, the particle is sucked out of the reaction chamber by a pump. According to surface energy theory, surface energy can be represented by a simple formula 4xcfx80r2xcex3, where xcex3 is the surface energy per unit area. For a plurality of smaller particles and one large particle having identical volume, the smaller particles have larger surface energy, resulting in rapid congregation, so that a smaller surface energy level is obtained. This explains why micro-particles within plasma congregate so rapidly.
Since negatively charged micro-particles may drop onto the low dielectric constant film and low dielectric constant film already has a lower density than a conventional silicate film, resistance against oxygen and nitrogen oxide is rather low. Ultimately, the low dielectric constant film may lose its low dielectric constant property.
Accordingly, one object of the present invention is to provide a method of fabricating a low dielectric constant film that can prevent surface oxidation of the dielectric film from oxygen plasma.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of forming a low dielectric constant film. A silicon substrate is provided. A main deposition is carried out inside a reaction chamber to form a carbon-rich low dielectric constant film over the substrate. The carbon-rich low dielectric constant film is formed by performing plasma chemical vapor deposition using plasma such as nitrogen oxide and nitrogen. After the formation of the dielectric film, the supply of nitrogen oxide to the reaction chamber is cut off while ammonia is passed into the reaction chamber so that the micro-particles over the dielectric film are purged. By adjusting the flow rate of ammonia, as well as the pressure and the plasma density inside the plasma reaction chamber, different ammonia plasma conditions are produced. Different plasma conditions of the ammonia are applied in sequence to clear away micro-particles on the dielectric film.
In this invention, ammonia plasma is used instead of nitrogen oxide and nitrogen plasma to carry out purging. The ammonia plasma can remove micro-particles from the surface of low dielectric constant film without causing any surface oxidation.
In addition, using different ammonia plasma conditions in the purging step prevents the rapid congregation of micro-particles within the plasma, in addition to keeping them from dropping onto the dielectric film. Hence, a quality carbon-rich low dielectric constant film is produced.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.